This invention relates to a navigation system for mobile robots. Robot guidance systems are implemented in many different forms. During its motion within an environment, the robot is set to move along predetermined paths. The robot verifies its own position along the path being taken by making odometric measurements. This means that sensors positioned at the locomotion means, i.e. the wheels, compute the distance travelled by the robot and any angular variations in orientation which may occur in its trajectory. Helping itself with this type of measurement, the robot is able to follow any type of trajectory. However, actually, the slack between moving mechanical parts, which cannot be calculated beforehand, slippage along the ground, ground roughness and other imperfections mean that discordance exist between the position calculated at a determined instant from the odometric measurements, and the position effectively reached at that moment by the robot. These evaluation errors incrementally add during the movement of the robot, which can hence at the end of its predetermined path be in a position totally different from that required.
It is therefore necessary to provide the robot with an autonomous system for monitoring its position within an environment, which whenever the odometrically estimated position is different form the effective position causes the odometric measurements to be updated to their correct values. This provides a cyclic check on the real position of the robot, together with a trajectory correction if a significant error is found. Hence the danger of the robot being in an erroneous position at the conclusion of its path is minimized.
In the past, different ways of making such a check have been proposed. One widely practised method is to insert into the environment or environments within which the robot is supposed to operate, both active and passive sensors located in predetermined positions known to the robot. Active sensors can be for example active beacons emitting coded signals. A passive sensor is located on the robot to sense the signals emitted by several beacons such that the robot navigation system can deduce its own position relative to them. The beacons are often coupled with RF (radiofrequency) emitters in order to transmit the position code associated with the beacon to the robot.
Other systems use energy emitting sensors located on board the robot, for example rotary laser scanners coupled with a photodiode. For this purpose a number of retroreflectors are positioned within the environment to reflect the signal originating from the rotary emitter.
The robot navigation system then calculates the robot position by suitable triangulation.
These known systems exhibit drawbacks and problems.
Firstly, as the number of active sensor or reflecting objects required for calculating the robot position is greater than or equal to three, the number of said sensors must be very large, so that at every reached position in the environment, the robot is able to simultaneously "see" at least three of said sensors or reflecting objects. If the environment is of relatively complex structure, the number of such sensors can become very large. This system is therefore particularly invasive of the integrity of the operational region.
In addition, if a laser is used, its introduction into a working environment causes safety problems if the emitted power exceeds determined levels. Consequently, is the emitted power has to be low, the useful operating distance becomes low as well, with loss of effectiveness. The object of the present invention is to develop a navigation system by which the position of the robot within the environment can be estimated in an unambiguous and simple manner, without finding the aforesaid problems.